Schistosoma mansoni is a parasitic helminth that lives in the blood vessels of humans. It infects 220 million persons in 76 different countries including Puerto Rico and the Santa Lucia Islands, US territories. Although the parasite lives in the host in an aerobic millieu, it depends for its survival on anaerobic glycolysis. Our philosophy is that the better our understanding of the physiology and biochemistry of the parasite, the better our chance of identifying unique targets that can be selectively influenced by prospective chemotherapeutic agents. In order to survive, S. mansoni must metabolize every 6 hours an amount of glucose equivalent to its dry weight. Inhibition of a rate limiting enzyme in glycolysis, such as phosphofructokinase, by chemotherapeutic agents (e.g., organic antimonial) is lethal to the parasites. This research focuses on a hormonal/transduction system discovered in our laboratory in S. mansoni and other trematodes that regulates glycolysis in these parasites. Serotonin is a hormone-like agent in S. mansoni. It stimulates glycolysis and glycogenolysis and activates adenylate cyclase, glycogen phosphorylase and phosphofructokinase. It has many of the same functions that epinephrine has in mammals. The transmembrane signalling system for serotonin is composed of serotonin receptors that are unique to the parasite; a GTP binding protein; adenylate cyclase, a c-AMP-dependent protein kinase and signal and target proteins(e.g., phosphofructokinase). In this proposal we plan to study in depth three components of the serotonin signalling system: phosphofructokinase, GTP binding proteins, and serotonin receptors. Since our first attempt to renew this grant, we have succeeded in cloning two components of the signalling system, the Gsa protein and phosphofructokinase. We will complete the structural and functional analysis of the Gsa clone. We will express the PFK gene in bacterial or insect cells and study the biochemical nature of the recombinant protein. We plan to continue our work on cloning the serotonin receptor from the parasites and on characterizing its molecular and biochemical properties. Our studies have more significance than their possible use for drug development. Characterization of the molecular components of this "primitive" signalling system contribute to our basic knowledge of transmembrane signal transduction.